In vitro activity of tigecycline and molecular characterization of extended-spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumoniae isolates from a university hospital in south-western Germany.

BACKGROUND

Extended-spectrum β-lactamase (ESBL)-producing organisms are spreading worldwide in hospital and community settings.

METHODS

A total of 328 unduplicated ESBL-producing Enterobacteriaceae isolated in 2008 and 2009 at the University Hospital of Tübingen were analysed retrospectively.

RESULTS

Escherichia coli (n = 253) and Klebsiella spp. (n = 46) were the most frequent ESBL-producing species. The ESBL rates among E. coli and Klebsiella spp. increased from 3.8 and 2.1%, respectively, in 2008, to 5.2 and 2.4%, respectively, in 2009. Two E. coli and 3 Klebsiella pneumoniae ESBL producers were non-susceptible to ertapenem, most likely due to loss of porins. Antimicrobial susceptibility testing of selected, molecularly characterized ESBL producers revealed susceptibility to tigecycline among 97.9% (191/195) of the E. coli and 78.8% (26/33) of the K. pneumoniae isolates. PCR analysis and sequencing showed the presence of CTX-M-type enzymes in 91.3% of the E. coli and 87.9% of the K. pneumoniae isolates, whereby bla(CTX-M-15) was the most frequent ESBL gene both in E. coli (50.0%) and K. pneumoniae (51.5%). Only 7 single cases of potential patient-to-patient transmissions of E. coli strains were observed.

CONCLUSIONS

Our data suggest that the increase in ESBL-producing E. coli and K. pneumoniae isolates at our hospital is mainly caused by growing import of Enterobacteriaceae harbouring CTX-M-type ESBLs.